Jacobi elliptic functions occur naturally in two contexts: in geometry as parametrization of the elipse similar to a parametrization of a circle and in physics/analysis, where they are connected to solutions of mathematical pendulum. We will consider the analytical approach, where we will look at the motivation from physics and definitions of the basic functions ${\rm sn}(x, k)$, ${\rm cn}(x, k)$ and ${\rm dn}(x, k)$. We shall then state and prove their general properties such as position of zeros, poles, periodicity, addition formulas etc. In the last chapter we prove three theorems from geometry using these properties.
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